Piston pump

ABSTRACT

The invention relates to a piston pump, in particular for an antilock and slip-controlled vehicle brake system. In order to embody a filter, the invention proposes providing a bushing of the piston pump with a bushing that encompasses it, wherein the bushing has beads on its ends, which are provided with grooves after the fashion of a knurling, through which incoming brake fluid flows between a wall of a pump bore and the bead into the piston pump and is therefore filtered.

PRIOR ART

The invention relates to a piston pump for a vehicle brake systemaccording to the preamble to the main claim.

Piston pumps of this kind are known, for example, as return feed pumpsfor antilock and/or traction controlled hydraulic vehicle brake systems.For example, reference is made to the piston pump disclosed by DE 41 07979 A1. The known piston pump has a pump housing with a pump bore whichencloses a piston so that it can move axially. The piston can be driveninto an axially reciprocating stroke motion in the pump bore by means ofa cam drive. The piston can be guided directly in the pump bore of thepump housing or, as in the known piston pump, can be guided in a bushinginserted into the pump bore. Furthermore, it is known to provide afilter for filtering fluid that is supplied by the piston pump.

ADVANTAGES OF THE INVENTION

The piston pump according to the invention, which has the features ofthe main claim, has a filter with a rough counter surface that restsagainst a surface that is smooth, for example, or is likewise rough. Asa result of the rough surface resting against the counter surface,channels are formed that are small in cross section, through which thefluid to be supplied is conveyed and thereby filtered. The roughness ofthe surface is selected so that the channels formed have a cross sectionthat corresponds to the size of through openings of filters for pistonpumps of this kind. The invention has the advantage that the filter canbe easily and inexpensively produced.

Advantageous embodiments and improvements of the invention disclosed inthe main claim are the subject of the dependent claims.

For example, the rough surface can have nubs or a fluting, it can bemanufactured as a knurling or so that it resembles a knurling (claim 2),wherein with a fluting or the like, attention must be paid that thefluting is not embodied extending lateral to the through flow directionof the fluid to be supplied so that the fluid is permitted to flowthrough.

In one embodiment of the invention, the filter is disposed in the pumpbore and the rough surface is formed so that it is complementary to thewall of the pump bore, wherein the wall of the pump bore constitutes thecounter surface against which the rough surface rests (claim 3).Complementary means that the rough surface and the wall of the pump borehave the same curvature. This embodiment of the invention has theadvantage that the filter is accommodated in a space-saving manner inthe pump bore and that the piston pump can be embodied as short instructure.

In an improvement according to claim 4, the piston pump has a bushingwhose outer circumference surface is rough at least on a part of thetotal surface area, and rests against the wall of the pump bore thatconstitutes the counter surface. This embodiment has the advantage thatno separate parts are necessary; in particular, the production andinstallation of a filter are no longer necessary.

Conversely, it is also possible to embody the wall of the pump bore asrough, at least on a part of the total surface area, wherein the bushingresting against the wall of the pump bore constitutes the countersurface (claim 7). The outer circumference surface of the bushing can besmooth or likewise rough in this embodiment of the invention.

The piston pump according to the invention is particularly provided as apump in a brake system of a vehicle and is used when controlling thepressure in wheel brake cylinders. The abbreviations ABS, TCS, ESP, orEHB are used for such brake systems, depending on the type of brakesystem involved. In the brake system, the pump serves for example toreturn brake fluid from one or a number of wheel brake cylinders to amaster cylinder (ABS) and/or to supply brake fluid from a storage tankinto one or a number of wheel brake cylinders (TCS, ESP, or EHB). Thepump is required, for example, in a brake system with wheel slip control(ABS or TCS) and/or a brake system serving as a steering aid (ESP)and/or an electrohydraulic brake system (EHB). With wheel slip control(ABS or TCS), for example a locking of the wheels of the vehicle duringa braking maneuver can be prevented when there is strong pressure on thebrake pedal (ABS) and/or a spinning of the driven wheels of the vehiclecan be prevented when there is strong pressure on the gas pedal (TCS).In a brake system that serves as a steering aid (ESP), a brake pressureis built up in one or more wheel brake cylinders independently of anactuation of the brake pedal or gas pedal, for example in order toprevent the vehicle from breaking out of the track desired by thedriver. The pump can also be used in an electrohydraulic brake system(EHB) in which the pump supplies the brake fluid into the wheel brakecylinder or cylinders if an electric brake pedal sensor detects anactuation of the brake pedal or in which the pump is used to fill areservoir of the brake system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in detail below in conjunction with aselected exemplary embodiment shown in the drawing.

FIG. 1 shows a 90°-angled axial section through a piston pump accordingto the invention along line I—I in FIG. 2, and

FIG. 2 shows a cross section through the piston pump along line II—II inFIG. 1.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The piston pump according to the invention, which is shown in thedrawing and is labeled as a whole with the reference numeral 10, has apump housing 12 with a straight, stepped pump bore 14. The pump housing12 is comprised of metal, in particular of pressure cast aluminum. Thepump housing 12 is part of a hydraulic block, otherwise not shown, of anantilock and traction controlled vehicle brake system. In addition tothe piston pump 10, other hydraulic components such as solenoid valves,damper chambers, and hydraulic accumulators are inserted into thehydraulic block and are hydraulically connected to each other and to thepiston pump 10. For the sake of clear depiction, only a fraction of thehydraulic block that encompasses the piston pump 10 is shown in thedrawings.

The pump bore 14 has a bushing 16 inserted into it, which ismanufactured out of plastic as an injection molded part and has abushing bottom 18 that is of one piece with it. A piston 20 made ofplastic is contained in the bushing 16 so that it can slide axially. Onan end disposed against the bushing 16, the piston 20 is sealed in thebushing 16 with a sealing ring 22 that is inserted into a piston groove24. On an end protruding from the bushing 16, the piston 20 is guidedwith a plastic guide ring 26 in the pump bore 14 and is sealed in thepump bore 14 with a sealing ring 28. The guide ring 26 and the sealingring 28 are inserted resting against each other into a step 30 of thepump bore 14 and are secured in the step 30 of the pump bore 14 by anend edge 32 of the bushing 16 oriented toward them. The piston 20 isembodied as a stepped piston, i.e. it is inserted and sealed in thebushing 16 on a greater diameter than at its end protruding from thebushing 16. Instead of the stepped piston 20, a simple piston can alsobe used which is guided and sealed on the same diameter at both of itsends (not shown).

In order to drive the piston 20 into an axial reciprocating strokemotion in the pump bore 14 and the bushing 16, the piston pump 10 has acam, which can be driven to rotate by an electric motor, on the end ofthe piston 20 protruding from the bushing 16, and the piston 20 ispressed against the circumference of this cam by a piston restoringspring 36 embodied as a helical compression spring, which is insertedinto the bushing 16 between the bushing bottom 18 and the piston 20.

As an inlet valve 38, the piston pump 10 according to the invention hasa spring-loaded check valve with a valve ball 40 as a valve closingbody. The valve ball 40 is pressed against a conical valve seat 44embodied centrally in the bushing bottom 18 by a valve closing spring 42embodied as a helical compression spring. The valve closing spring 42 issupported against a valve cage 46, which is provided with through flowopenings 48 for the brake fluid that is to be supplied by the pistonpump 10. The valve cage 46 is produced as a stamped and deep-drawn partmade of sheet metal. It has an annular disk-shaped spring plate 50 whichprotrudes radially outward, which the piston restoring spring 36 restsagainst and with which the piston restoring spring 36 presses the valvecage 46 against the bushing bottom 18. The piston restoring spring 36 isembodied as considerably stronger than the valve closing spring 42 ofthe inlet valve 38 so that it reliably holds the valve cage 46 incontact with the bushing bottom 18 counter to the force of the valveclosing spring 42 under all loads that occur during operation of thepiston pump 10.

The valve cage 46, which encloses the valve closing spring 42 and thevalve ball 40 of the inlet valve 38, is disposed on the side of thebushing bottom 18 oriented toward the piston 20, i.e. on the inside ofthe bushing 16. An inflow of brake fluid takes place by means of aninlet bore 52 in the pump housing 12, which feeds radially into the pumpbore 14 and also, by means of a cross-sectionally annular intermediaryspace between the bushing 16 and the pump bore 14, feeds into a crossconduit 54 which passes laterally through the bushing bottom 18. Due tothe angled sectional depiction in FIG. 1, the cross conduit 54 appearsto end in the middle of the bushing bottom 18; in actual fact, the crossconduit 54 passes laterally through the bushing bottom 18 as shown inFIG. 2. The cross conduit 54 is disposed on an end of the inlet valve 38remote from the piston 20. The cross conduit 54 has a short central bore56 leading from it to the inlet valve 38, which transitions into itsvalve seat 44.

An outflow takes place by means of an outlet bore 58, which passeslaterally through the bushing bottom 18 next to the cross conduit 54 andaxially parallel to the bushing 16 (FIG. 2). The outlet bore 58 feedswith a valve seat 60 of an outlet valve 62, which is embodied as aspring-loaded check valve. The outlet valve 62 has a valve ball 64 asthe valve closing body, which is pressed against the valve seat 60 by avalve closing spring 66 embodied as a helical compression spring.

The valve closing spring 66 is supported against a sealing cap 68, whichseals the pump bore 14 on an end remote from the cam element 34. Thesealing cap 68 is secured and sealed in a pressure-tight manner by meansof a circumferential caulking 70 of the pump housing 12.

By means of an annular conduit 72 between the pump housing 12 and thebushing bottom 18, brake fluid which has flowed from the piston pump 10by means of the outlet valve 62 travels into an outlet bore 74 which islet into the pump housing 12 radial to the pump bore 14.

The piston pump 10 according to the invention has a filter 76 which isdisposed in the inlet of the piston pump 10. The filter 76 has a bushing78 which is disposed at the level of the inlet bore 52 and encompassesthe bushing 16. The bushing 78 is provided with longitudinal ribs 80that are of one piece with the bushing 16 and the longitudinal ribs 80hold the bushing 78 spaced radially apart from the bushing 16. On eachof its two end faces, the bushing 78 has an outwardly protruding bead82, which rests with its circumference against a wall of the pump bore14. The circumference of the bead 82 is embodied as rough so that brakefluid flowing into the piston pump 10 at the circumference of this bead82 can flow between this bead and the wall of the pump bore 14. Sincethe through flow cross sections between the rough circumference of thebeads 82 and the wall of the pump bore 14 are small, the brake fluidflowing into the piston pump 10 is filtered as it flows through betweenthe bead 82 and the wall of the pump bore 14.

In the exemplary embodiment, the roughness of the circumference of thebeads 82 is constituted by means of small cross section grooves 84 thatpass axially through the bead 82 (FIG. 2). The grooves 84, which areproduced by means of the injection molding of the bushing 16 give thecircumference of the beads 82 the appearance of being knurled.

Brake fluid flowing in through the inlet bore 52 of the piston pump 10first travels on the outside of the bushing 78 of the filter 76, wherethe flow is divided and deflected to the beads 82 at both ends of thebushing 78. At the ends of the bushing 78, the brake fluid flows throughthe grooves 84 on the circumference of the beads 82 and is therebyfiltered. The part of brake fluid which flows through the grooves 84 ofthe bead 82 oriented toward the cam 34 is deflected 180° by an end edge86 of the bushing 78 and flows through between the inside of the bushing78 and the outside of the bushing 16 to the other end of the bushing 78where this part of the brake fluid is united with the other part ofbrake fluid which flows through the grooves 84 of the other bead 82 andfrom there, flows on the outside of the bushing 16 in the pump bore 14,traveling on into the cross conduit 54 in the bushing bottom 18.

The foregoing relates to the preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A piston pump for a vehicle brake system, havinga pump housing provided with a pump bore, which bore encloses a pistonfor movement axially, which piston can be driven into a reciprocatingstroke motion, said piston pump further having a filter for a fluid tobe supplied, said filter (76) having a rough surface portion (84), whichsurface portion rests against a counter surface, and the fluid to besupplied is conveyed between the rough surface portion (84) and thecounter surface.
 2. The piston pump according to claim 1, wherein therough surface portion (84) is embodied in the form of a knurling.
 3. Thepiston pump according to claim 1, wherein the filter (76) is disposed inthe pump bore (14) and the rough surface portion (84) has a shape thatis complementary to a wall of the pump bore (14), and further whereinthe wall of the pump bore (14) constitutes the counter surface againstwhich the rough surface portion (84) rests.
 4. The piston pump accordingto claim 2, wherein the filter (76) is disposed in the pump bore (14)and the rough surface portion (84) has a shape that is complementary toa wall of the pump bore (14), and further wherein the wall of the pumpbore (14) constitutes the counter surface against which the roughsurface portion (84) rests.
 5. The piston pump according to claim 1,wherein the piston pump (10) has a bushing (16), which is inserted intothe pump bore (14) and encloses the piston (20) so that the piston canmove axially, and at least one part of the outer surface (82) of thebushing (16) is roughened, and further wherein the roughened part of theouter surface (82) of bushing (16) constitutes the rough surface portion(84) with which the bushing (16) rests against the wall of the pump bore(14).
 6. The piston pump according to claim 2, wherein the piston pump(10) has a bushing (16), which is inserted into the pump bore (14) andencloses the piston (20) so that the piston can move axially, and atleast one part of the outer surface (82) of the bushing (16) isroughened, and further wherein the roughened part of the outer surface(82) of bushing (16) constitutes the rough surface portion (84) withwhich the bushing (16) rests against the wall of the pump bore (14). 7.The piston pump according to claim 3, wherein the piston pump (10) has abushing (16), which is inserted into the pump bore (14) and encloses thepiston (20) so that the piston can move axially, and at least one partof the outer surface (82) of the bushing (16) is roughened, and furtherwherein the roughened part of the outer surface (82) of bushing (16)constitutes the rough surface portion (84) with which the bushing (16)rests against the wall of the pump bore (14).
 8. The piston pumpaccording to claim 5, wherein the outer surface of the bushing (16) isroughened on a circumferential, axially limited section.
 9. The pistonpump according to claim 6, wherein the outer surface of the bushing (16)is roughened on a circumferential, axially limited section.
 10. Thepiston pump according to claim 7, wherein the outer surface of thebushing (16) is roughened on a circumferential, axially limited section.11. The piston pump according to claim 8, wherein the bushing (16) has acircumferential bead (82) that protrudes radially outward, whosecircumferential surface is roughened and constitutes the rough surfaceportion (84), and said bead rests against the wall of the pump bore(14).
 12. The piston pump according to claim 9, wherein the bushing (16)has a circumferential bead (82) that protrudes radially outward, whosecircumferential surface is roughened and constitutes the rough surfaceportion (84), and said bead rests against the wall of the pump bore(14).
 13. The piston pump according to claim 10, wherein the bushing(16) has a circumferential bead (82) that protrudes radially outward,whose circumferential surface is roughened and constitutes the roughsurface portion (84), and said bead rests against the wall of the pumpbore (14).
 14. The piston pump according to claim 1, wherein the pistonpump (10) has a bushing (16), which is inserted into the pump bore (14)and encloses the piston (20) so that the piston can move axially, atleast one part of the wall of the pump bore (14) is roughened, andfurther wherein the roughened part of the pump bore (14) comprises therough surface against which the bushing (16) rests with its outersurface to constitute the counter surface.
 15. The piston pump accordingto claim 2, wherein the piston pump (10) has a bushing (16), which isinserted into the pump bore (14) and encloses the piston (20) so thatthe piston can move axially, at least one part of the wall of the pumpbore (14) is roughened, and further wherein the roughened part of thepump bore (14) comprises the rough surface against which the bushing(16) rests with its outer surface to constitute the counter surface. 16.The piston pump according to claim 3, wherein the piston pump (10) has abushing (16), which is inserted into the pump bore (14) and encloses thepiston (20) so that the piston can move axially, at least one part ofthe wall of the pump bore (14) is roughened, and further wherein theroughened part of the pump bore (14) comprises the rough surface againstwhich the bushing (16) rests with its outer surface to constitute thecounter surface.
 17. The piston pump according to claim 5, wherein thepiston pump (10) has a bushing (16), which is inserted into the pumpbore (14) and encloses the piston (20) so that the piston can moveaxially, at least one part of the wall of the pump bore (14) isroughened, and further wherein the roughened part of the pump bore (14)comprises the rough surface against which the bushing (16) rests withits outer surface to constitute the counter surface.
 18. The piston pumpaccording to claim 8, wherein the piston pump (10) has a bushing (16),which is inserted into the pump bore (14) and encloses the piston (20)so that the piston can move axially, at least one part of the wall ofthe pump bore (14) is roughened, and further wherein the roughened partof the pump bore (14) comprises the rough surface against which thebushing (16) rests with its outer surface to constitute the countersurface.
 19. The piston pump according to claim 11, wherein the pistonpump (10) has a bushing (16), which is inserted into the pump bore (14)and encloses the piston (20) so that the piston can move axially, atleast one part of the wall of the pump bore (14) is roughened, andfurther wherein the roughened part of the pump bore (14) comprises therough surface against which the bushing (16) rests with its outersurface to constitute the counter surface.
 20. The piston pump accordingto claim 14, wherein the wall of the pump bore (14) is roughened on acircumferential, axially limited section.